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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Wind information display system user's manual

The Wind Information Display System (WINDS) provides flexible control through system-user interaction for collecting wind shear data, processing this data in real time, displaying the processed data, storing raw data on magnetic tapes, and post-processing raw data. The data are received from two asynchronous laser Doppler velocimeters (LDV's) and include position, velocity and intensity information. The raw data is written onto magnetic tape for permanent storage and is also processed in real time to depict wind velocities in a given spacial region.

Roe, J.↗
NASA NTRS1995

Solar wind composition

Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.

Ogilvie, K. W.↗
NASA NTRS1987

Solar cycle invariance in solar wind proton temperature relationships

The relationships between solar wind proton temperature and velocity and between temperature and momentum flux density at 1 AU are examined using National Space Science Data Center IMP 8 solar wind data obtained from late 1984 to early 1985. These relationships are compared with similar ones obtained from a variety of solar wind data spanning 14 years, from 1966 to 1980. It is found that these relationships, particularly the one between temperature and velocity, are very stable over the solar cycles from which these data were drawn. This suggests that the basic physical processes which accelerate and heat the solar wind have remained unchanged for the last 20 years.

Lopez, R. E.↗
NASA NTRS1990

Development of pitch angle anisotropy and velocity diffusion of pickup ion shell distribution by solar wind turbulence

The evolution of pitch angle anisotropy in initially isotropic spherical shell distribution of pickup ions subjected to a continuous influence of weak or moderate intrinsic solar wind turbulence is investigated using a physical model which assumes that the wave of the solar wind turbulence is propagating mainly in the direction parallel to the ambient magnetic field. It is shown that, because of the pitch angle dependence of the velocity diffusion process, a significant pitch angle anisotropy of pickup ion shell distribution develops in the early stage of the diffusion process. Although it is smeared out later on, the result can be of significant importance, especially if the pickup ion density is large, because the pitch angle anisotropy can excite collective instabilities and increase the wave level, thus accelerating the diffusion process.

Yoon, Peter H.↗
NASA NTRS1980

Hourly average values of solar wing parameters (flow rate and ion temperatures) according to data of measurements of the Venera-9 and Venera-10 automatic interplanetary stations on an Earth-Venus during the period June 1975 - April 1976

Four electrostatic analyzers with channel electron multipliers as detectors were used to measure solar wind ionic flow. The axes of the fields of vision of two of these analyzers were directed along the axis of the automatic interplanetary station, oriented towards the Sun, while the other two were turned in one plane at angles of +15 deg and -15 deg. The full hemisphere of the angular diagram of each analyzer was approximately 5 deg. The energetic resolution was approximately 6%, and the geometric energy was 0.002 sq cm ave. keV. Each analyzer covered an energetic range of approximately 10 in eight energetic intervals. Spectral distributions were processed in order to obtain the velocity and temperature of the protons. Tabular data show the hour interval (universal time) and the average solar wind velocity in kilometers per second.

Vaysberg, O. L.↗
NASA NTRS1985

One-dimensional kinematics of particle stream flow with application to solar wind simulation

A simple kinematic method for determining the particle velocity distribution of a model solar wind for which the spatial distribution of particles is given as a function of particle travel time has been developed by Hakamada and Akasofu (1982). Here their method is formalized mathematically and an inverse procedure for determining the particle distribution from a given velocity distribution is derived. This inverse procedure is then applied to a simulated velocity distribution obtained from an MHD finite difference code.

Olmsted, C.↗
DOE OSTI2011

DIRECTIONAL ALIGNMENT AND NON-GAUSSIAN STATISTICS IN SOLAR WIND TURBULENCE

The magnetic and velocity field fluctuations in magnetohydrodynamic turbulence can be characterized by their directional alignment and induced electric field. These manifest as coherent spatial correlations which are measures of Alfvenicity and turbulence cascade strength, respectively. Solar wind observations and direct numerical simulations find that these distinctive correlations, caused by rapid relaxation processes that act to suppress nonlinearity, occur in localized spatial patches. This cellularization of magnetofluid turbulence is inconsistent with a superposition of Gaussian fields and could be related to spatial intermittency or other non-Gaussian statistics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

POWER ANISOTROPY IN THE MAGNETIC FIELD POWER SPECTRAL TENSOR OF SOLAR WIND TURBULENCE

We observe the anisotropy of the power spectral tensor of magnetic field fluctuations in the fast solar wind for the first time. In heliocentric RTN coordinates, the power in each element of the tensor has a unique dependence on the angle between the magnetic field and velocity of the solar wind ({theta}{sub B}) and the angle of the vector in the plane perpendicular to the velocity ({phi}{sub B}). We derive the geometrical effect of the high speed flow of the solar wind past the spacecraft on the power spectrum in the frame of the plasma P(k) to arrive at the observed power spectrum P(f, {theta}{sub B}, {phi}{sub B}) based on a scalar field description of turbulence theory. This allows us to predict the variation in the {phi}{sub B} direction and compare it to the data. We then transform the observations from RTN coordinates to magnetic-field-aligned coordinates. The observed reduced power spectral tensor matches the theoretical predictions we derive in both RTN and field-aligned coordinates, which means that the local magnetic field we calculate with wavelet envelope functions is an accurate representation of the physical axis of symmetry for the turbulence and implies that on average the turbulence is axisymmetric. We also show that we can separate the dominant toroidal component of the turbulence from the smaller but significant poloidal component and that these have different power anisotropy. We also conclude that the magnetic helicity is anisotropic and mostly two dimensional, arising from wavevectors largely confined to the plane perpendicular to B .

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1993

Calibrating Airplane Instrumentation To Measure Winds

Elaborate combination of techniques used to calibrate wind-measuring instrumentation aboard F104 airplane. Obtains wind profiles more rapidly. Airplane equipped with standard NACA research nose boom, including pressure probes and flow vanes yielding data on static and total pressures, angle of attack, and angle of sideslip. Has ring-laser-gyroscope inertial reference unit, giving linear and angular velocities, linear acceleration, and orientation of airplane. Body-mounted total-temperature sensor also used. Improved method of calibration devised to determine whether winds aloft at and shortly after time of measurement allow safe launch of Space Shuttle. Proves beneficial in other safety- or research-oriented applications in which wind velocities over range of altitudes must be determined in nearly real time.

Haering, Edward A., Jr.↗
NASA NTRS1993

WINDII, the wind imaging interferometer on the Upper Atmosphere Research Satellite

The WIND imaging interferometer (WINDII) was launched on the Upper Atmosphere Research Satellite (UARS) on September 12, 1991. This joint project, sponsored by the Canadian Space Agency and the French Centre National d'Etudes Spatiales, in collaboration with NASA, has the responsibility of measuring the global wind pattern at the top of the altitude range covered by UARS. WINDII measures wind, temperature, and emission rate over the altitude range 80 to 300 km by using the visible region airglow emission from these altitudes as a target and employing optical Doppler interferometry to measure the small wavelength shifts of the narrow atomic and molecular airglow emission lines induced by the bulk velocity of the atmosphere carrying the emitting species. The instrument used is an all-glass field-widened achromatically and thermally compensated phase-stepping Michelson interferometer, along with a bare CCD detector that images the airglow limb through the interferometer. A sequence of phase-stepped images is processed to derive the wind velocity for two orthogonal view directions, yielding the vector horizontal wind. The process of data analysis, including the inversion of apparent quantities to vertical profiles, is described.

Shepherd, G. G.↗
NASA NTRS1979

Evidence for vertical motions in the equatorial middle atmosphere

The Diurnal Experiment, which took place in March 1974, offers a unique data set for use in studying vertical velocities in the equatorial stratosphere and mesosphere. Application of the standard thermodynamic vertical velocity equation along with a generalized thermal wind relation reveals magnitudes of vertical velocities ranging from 1-2 cm/s in the lower stratosphere to 10-15 cm/s in the lower mesosphere. Diurnal and semidiurnal tidal modes are quite apparent and, in agreement with tidal theory, the amplitudes of the oscillations increase with height. Inspection of time cross sections and use of Fourier analysis indicates vertical wavelengths on the order of 8-16 km. These results suggest that modification of temperature and wind profiles in the stratosphere and lower mesosphere on an hourly basis can be quite significant. The analysis also suggests the presence of unresolved vertical winds on both longer and shorter time scales than the principal tidal components.

Weisman, M. L.↗
NASA NTRS2002

The Winds of B Supergiants

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasizes the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M qi) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in turns of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, Derck↗
NASA NTRS1983

The velocity and the density spectrum of the solar wind from simultaneous three-frequency IPS observations

Density inhomogeneities in the solar wind cause fluctuations regarding the emission of small diameter radio sources. Such fluctuations are called interplanetary scintillation (IPS). IPS has been studied to obtain information on both the solar wind and on the radio sources. In the present investigation it is attempted to extract information about the solar wind from simultaneous IPS observations at three radio frequencies and a single antenna. Data were recorded at frequencies of 270 MHz, 340 MHz, and 470 MHz on a 91 m telescope. Five different radio sources were observed. The observations are compared with theoretical predictions for spectra, cross-spectra, and cross-correlations using weak scattering theory and various models for the wavenumber spectrum of density inhomogeneities in the solar wind. Good fits are obtained over the observed wavenumbers to a spectrum modeled as a power law.

Scott, S. L.↗
NASA NTRS2004

Density, Velocity and Ionization Structure in Accretion-Disc Winds

This was a project to exploit the unique capabilities of FUSE to monitor variations in the wind- formed spectral lines of the luminous, low-inclination, cataclysmic variables(CV) -- RW Sex. (The original proposal contained two additional objects but these were not approved.) These observations were intended to allow us to determine the relative roles of density and ionization state changes in the outflow and to search for spectroscopic signatures of stochastic small-scale structure and shocked gas. By monitoring the temporal behavior of blue-ward extended absorption lines with a wide range of ionization potentials and excitation energies, we proposed to track the changing physical conditions in the outflow. We planned to use a new Monte Carlo code to calculate the ionization structure of and radiative transfer through the CV wind. The analysis therefore was intended to establish the wind geometry, kinematics and ionization state, both in a time-averaged sense and as a function of time.

Sonneborn, George↗
NASA NTRS1995

Velocity Variations in the High-latitude Solar Wind

This is an extended abstract of a paper submitted for publication elsewhere [Neugebauer et al., 1995]. During 1994, the Ulysses spacecraft continuously sampled the properties of the solar wind from the south polar coronal hole. At latitudes poleward of 65øS, there was no longer any systematic variation of the solar wind with longitude [Phillips et al., 1995]. Thus any variations in the plasma parameters were intrinsic to the coronal hole flow rather than being caused by varying distances from the coronal-hole boundary.

High-Latitude↗
NASA NTRS2002

The Winds of B Supergiants

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasises the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters, but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M (dot) q(sub i)) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in terms of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, D.↗
NASA NTRS1988

The anomalous C 4 intensity ratio in symbiotic stars

The C IV lambda lambda 1548.2,1550.8 resonance doublet in a symbiotic stars was shown to exhibit anomalous line intensity ratios in which I (lambda 1548.2)/I(lambda 1550.8) less than 1, or less than the optically-thick limit of unity. The R Aquarii-central HII region and RX Puppis exhibit this phenomena. The I(lambda 1548.2)/I(lambda 1550.8) ratio in RX Puppis is found to vary inversely with the total C IV line intensity, and with the FES-visual light, as the object declined over a 5 yr period following a brightening in UV and optical emission which peaked in 1982. This doublet intensity behavior could be explained by a wind which has a narrow velocity range of 600 approx. less than sup v wind approx. less than 1000 km/sec, or by the pumping of the Fe II (mul. 45.01) transition a sup 4 F sub 9/2 - y sup 4 H(o) sub 11/2 by C IV lambda 1548.2, which effectively scatters C IV photons into the Fe II spectrum in these objects.

Michalitsianos, A. G.↗
DOE OSTI2011

SPECTRAL SCALING LAWS IN MAGNETOHYDRODYNAMIC TURBULENCE SIMULATIONS AND IN THE SOLAR WIND

The question is addressed as to what extent incompressible magnetohydrodynamics can describe random magnetic and velocity fluctuations measured in the solar wind. It is demonstrated that distributions of spectral indices for the velocity, magnetic field, and total energy obtained from high-resolution numerical simulations of magnetohydrodynamic turbulence are qualitatively and quantitatively similar to solar wind observations at 1 AU. Both simulations and observations show that in the inertial range the magnetic field spectrum E{sub b} is steeper than the velocity spectrum E{sub v} with E{sub b} {approx}> E{sub v} and that the magnitude of the residual energy E{sub R} = E{sub v} - E{sub b} decreases nearly following a k{sup -2}{sub perpendicular} scaling.

79 ASTRONOMY AND ASTROPHYSICS↗